Most DC-to-DC converters use switching circuitry based on pulse width modulation (PWM) to convert an input DC voltage to an output DC voltage. The ratio of the pulse widths of the PWM signal to the period of the PWM signal is proportional to the DC output voltage. The trend in DC-to-DC power conversion is towards very high switching frequencies in the converters, which requires very low periods in the PWM signals. Some applications, including converters, require that the switching operate with a fixed PWM frequency.
Conventional analog controlled PWM generators rely on saw-tooth signals to generate the PWM signals. The saw-tooth signals are compared to a reference voltage, wherein the resulting signal is a PWM signal having pulse widths that are proportional to the reference voltage. These conventional PWM generators are limited in their ability to generate narrow pulses in a jitter-free fashion. System noise and parasitic elements impact the ability of a PWM generator to develop narrow pulses suitable for power conversion at high conversion frequencies.